The First Detailed Abundances for M Giants in the Inner Bulge from Infrared Spectroscopy

We report the first abundance analysis of 17 M giant stars in the inner Galactic bulge at ( l , b ) = (0°, -1°), based on R = 25,000 infrared spectroscopy (1.5-1.8 μm) using NIRSPEC at the Keck telescope. Based on their luminosities and radial velocities, we identify these stars with a stellar population older than 1 Gyr. We find the iron abundance ⟨[Fe/H]⟩ = -0.22 ± 0.03, with a 1 σ dispersion of 0.14 ± 0.024. We also find the bulge stars have an enhanced [α/Fe] abundance ratio at the level of +0.3 dex relative to solar stars, and low ⟨ 12 C/ 13 C⟩ ≈ 6.5 ± 0.3. The derived iron abundance and composition for this inner bulge sample is indistinguishable from that of a sample of M giants our team has previously studied in Baade's window ( l , b ) = (0.9, -4). We find no evidence of any major iron abundance or abundance ratio gradient between this inner field and Baade's window.